This invention relates to flexible recording diskettes used for the storage of data in computer systems.
Flexible diskettes, commonly termed floppy disks, are commonly used for data storage in connection with computer systems. A typical flexible diskette includes a flexible annular recording disk rotatably encapsulated in a soft flexible jacket. The jacket is normally provided with a pair of aligned central apertures to permit the inner periphery of the recording disk to be clamped to the rotating spindle of an associated disk drive. In addition, the jacket is also typically provided with a pair of elongated radially extending apertures to afford access to the annular recording band on one or both sides of the flexible disk, so that a transducer and pressure pad (in a single-sided drive) or a pair of co-acting transducers (in a double-sided drive) may contact the surface of the disk during data storage or retrieval. Further, a pair of substantially annular wiping liners are typically adhered to the inner jacket surfaces to remove contaminant particles from the disk surfaces as the disk revolves within the jacket. To assist in this wiping action, the associated disk drive is typically provided with a pressure shoe or equivalent arrangement which acts on one or both outer surfaces of the diskette jacket to press the wiping material against the disk surface with sufficient force to promote the wiping action without substantially increasing the sliding friction between the disk surface and the inner liner material, i.e., without adversely affecting the ability of the disk to rotate within the jacket.
For reliability in performance, it is highly important that the position of the disk recording surface relative to the disk drive transducer, termed the disk operating plane, be predictable to a high degree. Consequently, well-designed disk drives for flexible diskettes include mechanical elements which serve to define the disk operating plane. In some disk drives, these elements include a stable reference surface and a mechanical shoe for biasing the diskette onto the reference surface.
Although originally designed with a diameter of 8", the second generation of commercially popular flexible diskettes was designed with a diameter of 51/4". This trend toward decreasing diametral dimensions has continued to the third generation of flexible diskettes, which are designed with a diameter of 31/2" or less. However, the reduction in size represented by the currently dimensioned micro-floppy diskette has aggravated some problems encountered with the grosser sized flexible diskettes and has introduced additional problems.
Due to the relatively small dimensions of the micro-floppy diskette, the track density required to provide reasonable storage capability has been increased from a maximum of about 100 tracks per inch for the 51/4" diskette to 135 tracks per inch for the 31/2" micro-floppy diskette. This increased track density requires either narrower tracks or more closely spaced tracks, which requires more stable disk media. Unfortunately, due to the relatively small size of the micro-floppy diskette, the potential for extreme thermal variations within the enclosure defined by the jacket has increased. In addition, the use of a metal hub secured to the inner margin of the disk media as the spindle mounting mechanism also increases the potential for thermal variations in the disk media due to the high thermal conductivity of the hub material as well as the intimate coupling with the disk.
Another problem aggravated by the reduction in size represented by the micro-floppy disk is that of particle contamination within the diskette jacket and handling damage to the disk media. Since the micro-floppy diskette is small enough to fit conveniently into a shirt or jacket pocket, it is much more portable than grosser sized disks and susceptible to more handling damage, and much more likely to be subject to particle contamination through the elongated access apertures.
The most popular micro-floppy diskette design at present attempts to reduce the contamination and handling damage problem by enclosing the disk in a relatively rigid plastic jacket provided with an externally mounted reciprocable shutter designed to cover the elongated access apertures when the disk is not in use. The use of the relatively rigid jacket, however, effectively precludes the use of an external pressure pad to promote the disk surface wiping function afforded by the liner material. In order to attempt to overcome this deficiency, a flexible tab is provided in the interior of the jacket to provide a biasing force between the inner jacket surface and the liner surface to attempt to force the liner material against the disk surface. This arrangement, however, is markedly inferior to the external pressure pad arrangement noted above. The use of the reciprocable shutter, which is fabricated from metal, introduces another potential source of thermal instability to the disk media, given the high thermal conductivity of the shutter material. In addition, however, the external shutter, being substantially thicker than the disk jacket, introduces a source of potential damage to the precisely contoured transducer surfaces in the associated disk drive, when the diskette is inserted and removed from the drive. Moreover, the potential for contamination and handling damage still remains with this design, since the shutter may be manually reciprocated to the open position and, in one version of the design, the shutter is provided with an automatic locking mechanism which locks the shutter in the open position when manually operated.
Perhaps the greatest problem presently encountered with the current micro-floppy diskette design is that of disk operating plane variation. As noted above, in order to function in an optimum fashion, the disk media should ideally rotate in a plane that is well defined with respect to the position of the transducer in the associated disk drive. Any deviation from this ideal disk operating plane adversely affects the ability of the disk/transducer combination to reliably record and read data on and from the disk recording surface. With grosser sized diskettes, the disk operating plane could be well defined by means of an external pressure shoe or equivalent mechanism to deform the disk media through the flexible jacket just upstream of the transducer location, thereby ensuring the proper positioning of the disk media in the disk operating plane. Due to the use of the relatively rigid external jacket, however, this provision is not possible in the current design.